In a DC-DC converter widely used as an example of a power source circuit, a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) for a high side and a power MOSFET for a low side are connected in series. The power MOSFET for high side has a switch function for control of the DC-DC converter, and the MOSFET for low side has a switch function for synchronous rectification. These two power MOSFETs are alternately turned ON/OFF in synchronization, thereby converting power source voltage.
Such a DC-DC converter is described, for example, in Japanese Unexamined Patent Application Publication (Tokuhyo) No. 2003-528449 (Patent Document 1), and it discloses a structure in which a power MOSFET for high side, a power MOSFET for low side, a driver circuit which drives these power MOSFETs, and an input capacitor are contained in the same package.
Further, Japanese Patent Application Laid-Open Publication No. 2002-217416 (Patent Document 2) discloses a package structure in which a power MOSFET for high side constituting a DC-DC converter is formed of a horizontal power MOSFET, a power MOSFET for low side is formed of a vertical power MOSFET, and these power MOSFETs are mounted on a common frame.